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Her new book, "The Scientific American Day in the Life of Your Brain," tracks what's happening in your brain during the average day -- the best food to fuel you through your waking hours (she recommends complex carbohydrates and lean protein; "be wary of fad diets that focus on one food type or group. These can wreak havoc by upsetting your body and brain balance"), when the peak time for exercise is ("Some research shows body temperature may peak around late afternoon or early evening, so that might be the best time to work out" but we are individuals so we'd "do best to keep a kind of daily energy diary" to see when we're at our personal best) and more in the interview below.

That's Fit: How does self-control suck your energy?

Judith Horstman: Like most activities, self-control takes energy, and that requires fuel. And yes, not doing something is an activity. A part of your brain -- usually the reasoning thinking part -- has to expend energy to not react to stimulus such as a luscious piece of calorie-laden pie. As one researcher says in the book, willpower is more than a metaphor: It's an expensive metabolic activity. That seems doubly unfair, doesn't it? You need to take in fuel (eat) to control your urge to eat.

TF: So if self-control doesn't work, what can you do to prevent overeating?

J.H.: Well, we don't say self-control doesn't work -- just that it isn't easy. I'm not a nutrition expert (and no, I won't tell you how much weight I gained sitting in front of the computer to write this book), but the research I read supports much of the advice we get from many diet gurus and from your mom: Don't skip meals, because you need to ingest "fuel" on a regular basis to keep your brain neurotransmitters and other body chemistry stable -- and to help keep you from getting so hungry, you practically invite overeating. Regular meals (or perhaps many small meals) throughout the day seem to help your brain most.

And choose your "fuel" carefully: An apple and a piece of string cheese is going to do your brain more good than a bunch of empty calories from a late-afternoon cannelloni (my ultimate weakness, by the way). And from what I'm finding in other research, a soda (diet or regular) may be one of the worst things for your weight and your brain: We're talking about putting a 9-cent tax on soda in my state, California.

By the way, exercise is one of the very best things you can do for your brain and your body: It promotes brain cell production, brain health in general and a healthier you.

TF: Why do we crave food even if we're not hungry?

J.H.: That's your old amygdala -- the fight-or-flight survival-oriented center of your brain -- always looking out for your best interests -- or what your primitive brain thinks is in your best interest, like that piece of double chocolate cake. Remember, it gets that sated happy feeling when you eat and then settles down just like your family after a big Thanksgiving dinner. But when your dopamine (the feel-good neurotransmitter) levels are off, the eating urge continues. Overeating can become an addiction.

If you're already overweight, you could be at higher risk: Some research shows the number of dopamine receptors in the brains of overweight people is closely related to their BMI (body mass index): The higher the BMI, the heavier you are, and the fewer dopamine receptors you have, which means very overweight people could have a dopamine shortage, which makes them constantly seek reward-stimulants in the form of food. This sets up a vicious cycle that's similar to dopamine-seeking in drug addicts: An addict's brain notes the dopamine surge [during drug use], then compensates for the excess dopamine by reducing the number of dopamine receptors which triggers a need for more dopamine.

The good news is that if the brain's yen for food and its Joneses for drugs are very much the same, then similar medications and behavioral control might play a role in controlling both kinds addiction.

In an earlier "3 Questions With..." interview, the former FDA Commissioner David A. Kessler and author of "The End of Overeating" talks about his own issues with food and self-control.